1. Field of the Invention
The present invention relates generally to vehicle system start controllers and particularly to vehicle system start controllers capable of high reliably starting and stopping vehicle systems.
2. Description of the Background Art
Vehicle systems are typically started by operating an ignition switch operated by inserting an ignition key into a key hole and rotating the key to a prescribed position. The ignition switch assumes an OFF position allowing the ignition key to be inserted and removed, an accessory (ACC) position allowing car audio and other similar accessory electrical equipment to conduct, an ON position energizing the engine's ignition system, and an engine start (ST) position energizing the starter.
To start a vehicle system, for example as disclosed in Japanese Patent Laying-Open No. 2000-050513, the ignition switch is operated to assume the ON position and in response an IG signal of the logical high level is input to a controller of a power supply control unit. In response to the IG signal of the high level the power supply control unit electrically connects a relay switching between supplying and stopping power to a load. Thus a battery's power supply is supplied to a plurality of loads including units electrically controlling an engine, an A/T, a meter and the like. The control units all receive power supplied from the battery to control the vehicle's state.
To stop the vehicle system the ignition switch is operated to assume the OFF position and in response the IG signal of the logical low level is input to the controller of the power supply control unit. The power supply control unit receives the IG signal of the low level and in response electrically disconnects the relay to interrupt the power supplied from the battery to the plurality of loads.
If the vehicle system thus configured has the ignition switch failed for example by a break, the IG signal is fixed at the low level and the vehicle system cannot be started. As such, the ignition switch is required to reliably turn on.
For an analog signal circuit outputting a desired signal voltage for example for vehicular electronic control equipment a defective break detection device including a hold circuit holding a signal voltage output from the analog signal circuit and a discharge circuit causing an electric charge distributed in the analog signal circuit to be discharged to the ground is disclosed, for example as described in Japanese Patent Laying-Open No. 2004-020315.
As described in the document, the hold circuit is a charge circuit including a switch, a capacitor and the like. When the hold circuit receives an instruction from an instruction portion to take in the signal voltage the hold circuit turns on the switch and holds the signal voltage in the capacitor. When the signal voltage held in the capacitor is output to an A/D converter, it is A/D converted and output to the instruction portion.
Furthermore, the defective break detection device employs a discharge circuit to discharge simultaneously the electrical charge distributed in the analog signal circuit and the signal voltage held in the hold circuit, and after they are discharged the device holds in the hold circuit a signal voltage output from the analog signal circuit and from a result of A/D converting the held signal voltage detects whether the analog signal circuit has a defective break.
The above described defective break detection device that has the hold circuit holding a signal voltage can detect whether the analog circuit has a defective break. If the hold circuit itself has the switch for example welded and thus failed, however, the signal voltage held by the hold circuit and that output from the analog signal circuit do not match, and the vehicle will not be controlled normally. Accordingly, to provide a signal voltage increased in reliability, the hold circuit must be detected as well as the analog signal circuit for failure.
In particular, if a vehicle system start controller has such a hold circuit mounted therein and in response to the ignition switch being operated to assume the ON position the hold circuit receives the IG signal of the high level, the hold circuit holds the logical level and outputs it to the instruction portion, or an electrical control unit (ECU). If the hold circuit is failed and the logical level is fixed at the high level, operating the ignition switch to assume the OFF position cannot stop the vehicle system. In other words, the hold circuit cannot sufficiently ensure that the ignition switch can be operated to reliably turn off.